Population SD (σ) — use when your data represents the entire population (every member). Divides by n.
Sample SD (s) — use when your data is a sample drawn from a larger population (most common in practice). Divides by n−1. This is what Excel's STDEV function calculates.
For large datasets the difference is negligible. For small samples (under 30), always use sample SD.
What does a high standard deviation mean?
A high SD means the values are spread widely from the mean. A low SD means they are clustered close to the mean. A SD of zero means all values are identical.
Can I paste from Excel?
Yes — copy a column of numbers from Excel or Google Sheets and paste directly into the box.